Get-tough laws that have put more teenagers in adult prisons since the early '90s conflict with a wave of new research suggesting how children can be set straight and society protected at the same time.

At a two-day summit starting Thursday in Washington, leading researchers will meet with juvenile justice decision-makers — directors of state juvenile justice systems, judges, prosecutors and defense attorneys — to discuss how the new evidence should affect treatment of teen offenders.

"We know so much more about the adolescent brain and behavior than we used to, and we want to get these facts into the hands of people who can make a difference," psychologist Laurence Steinberg says. He heads a network of researchers and juvenile-justice workers financed by the MacArthur Foundation, which sponsored the meeting.

Since 1992, every state but Nebraska has made it easier to try juveniles as adults, and most states have legalized harsher sentences. Many states limit judges' discretion, sending all teens who commit serious offenses to adult courts, or allowing prosecutors to opt for adult prosecution.

That sounds reasonable, but it can be unfair, says Kimberly O'Donnell, chief judge of the Juvenile and Domestic Relations District Court in Richmond, Va. She points to 14-year-olds tried as adults for "assault by a mob" — in effect, ganging up on and hurting a child at school.

"And once you're tried as an adult, you're always an adult, which can have awful consequences," she says.

For example, if these teens are arrested again, prosecutors can use the threat of lengthy prison sentences as leverage to gain a plea bargain agreement that might not be in a child's interest, O'Donnell says.

There's firm evidence that teens prosecuted as adults are much more likely to commit crimes when they get out than comparable young people tried as juveniles, says Shay Bilchik, president and CEO of the Child Welfare League of America.

That's not to say kids don't commit serious crimes before landing in adult jails. Some even score in the psychopathic range on written tests that predict which adults are likely to commit future crimes. These tests are sometimes used in deciding whether young people should get severe punishments or be tried as adults, says psychologist Elizabeth Cauffman of the University of California-Irvine.

She says it's a dubious practice. Her studies show that adolescents tend to move away from this psychopath profile when they're tracked for a couple of years, while adult scores are usually stable.

Some hallmarks of psychopathy — thrill-seeking, impulsivity, failure to accept responsibility — are all too familiar to parents of teenagers, Cauffman says. In effect, youths grow out of this behavior.

Many younger children aren't even competent to stand trial because they don't understand the trial process or can't make decisions about pleas, says Thomas Grisso, a psychologist at the University of Massachusetts Medical School in Worcester. He has developed guidelines to determine juvenile competence and is training U.S. juvenile court workers in using them.

New findings of other MacArthur network scientists challenge common assumptions about teenage criminals. For example, a study that has tracked 1,355 serious offenders for three years finds that less than 10% of those involved in a lot of criminal activities at the outset continued to be heavily involved over the years. "A lot of policy is driven by the view that if a kid does a felony assault, he must be a bad actor from here on forward," says study leader Edward Mulvey of the University of Pittsburgh Medical School.

Still, 57% had at least one more arrest within two years. "Plus, we know arrests represent only the tip of the iceberg. Who really knows how much else they did that they weren't caught for?" asks Adrian Raine, a psychologist at the University of Southern California who studies criminal behavior.

Long-term studies of highly aggressive children suggest that some are headed for a life of violent crime and should be locked up early because they're dangerous, he says. Brain damage or family qualities may cause their behavior, Raine says.

"But it's naive to think many of these very violent kids are going to stop, and we don't need to be protected from them."

In Mulvey's study, better parenting and long-term treatment for drug or alcohol abuse correlated with less criminal behavior.

Bilchik, a former prosecutor of juvenile cases in Miami for 16 years and former head of the federal Office of Juvenile Justice and Delinquency Prevention, can understand why research has been slow to translate into action.

"When you've got a kid in front of you who's done a vicious armed robbery with a beating, it's different than an intellectual argument about what works," Bilchik says. "Prosecutors think, 'Can I really make myself try him as a juvenile? Can I even get permission from my boss?' "

Sometimes prosecutors know a juvenile system has scant mental health treatment or rehabilitation, and they'd rather lock up a dangerous teen with adults than risk a slap on the wrist, Bilchik says. And often there's little follow-up monitoring by youth workers when troubled young people are let out. Still, he says adult prisons, despite their short-term appeal, aren't usually the long-term answer. "We have the research that tells us what to do. The tragedy is, we're not capitalizing on it."